Reich P B, Walters M B, Kloeppel B D, Ellsworth D S
Department of Forest Resources, University of Minnesota, 55108, St. Paul, MN, USA.
Department of Forestry, University of Wisconsin, 53706, Madison, WI, USA.
Oecologia. 1995 Sep;104(1):24-30. doi: 10.1007/BF00365558.
The relationship between photosynthetic capacity (A ) and leaf nitrogen concentration (N) among all C species can be described roughly with one general equation, yet within that overall pattern species groups or individual species may have markedly different A -N relationships. To determine whether one or several predictive, fundamental A -N relationships exist for temperate trees we measured A , specific leaf area (SLA) and N in 22 broad-leaved deciduous and 9 needle-leaved evergreen tree species in Wisconsin, United States. For broad-leaved deciduous trees, mass-based A was highly correlated with leaf N (r =0.75, P<0.001). For evergreen conifers, mass-based A was also correlated with leaf N (r =0.59, P<0.001) and the slope of the regression (rate of increase of A per unit increase in N) was lower (P<0.001) by two-thirds than in the broad-leaved species (1.9 vs. 6.4 μmol CO g N s), consistent with predictions based on tropical rain forest trees of short vs. long leaf life-span. On an area basis, there was a strong A -N correlation among deciduous species (r =0.78, P<0.001) and no correlation (r =0.03, P>0.25) in the evergreen conifers. Compared to deciduous trees at a common leaf N (mass or area basis), evergreen trees had lower A and SLA. For all data pooled, both leaf N and A on a mass basis were correlated (r =0.6) with SLA; in contrast, area-based leaf N scaled tightly with SLA (r =0.81), but area-based A did not (r =0.06) because of low A per unit N in the evergreen conifers. Multiple regression analysis of all data pooled showed that both N (mass or area basis) and SLA were significantly (P<0.001) related to A on mass (r =0.80) and area (r =0.55) bases, respectively. These results provide further evidence that A -N relationships are fundamentally different for ecologically distinct species groups with differing suites of foliage characteristics: species with long leaf life-spans and low SLA, whether broad-leaved or needle-leaved, tend to have lower A per unit leaf N and a lower slope and higher intercept of the A -N relation than do species with shorter leaf life-span and higher SLA. A single global A -N equation overestimates and underestimates A for temperate trees at the upper and lower end of their leaf N range, respectively. Users of A -N relationships in modeling photosynthesis in different ecosystems should appreciate the strengths and limitations of regression equations based on different species groupings.
所有C植物物种的光合能力（A）与叶片氮浓度（N）之间的关系大致可用一个通用方程来描述，但在这一总体模式中，物种组或单个物种的A - N关系可能有显著差异。为了确定温带树木是否存在一个或几个预测性的、基本的A - N关系，我们在美国威斯康星州测量了22种阔叶落叶树种和9种针叶常绿树种的A、比叶面积（SLA）和N。对于阔叶落叶树，基于质量的A与叶片N高度相关（r = 0.75，P < 0.001）。对于常绿针叶树，基于质量的A也与叶片N相关（r = 0.59，P < 0.001），且回归斜率（N每增加一个单位A的增加速率）比阔叶树种低三分之二（P < 0.001）（1.9对6.4 μmol CO₂ g⁻¹ N⁻¹ s⁻¹），这与基于叶片寿命短与长的热带雨林树木的预测一致。在面积基础上，落叶树种之间A - N相关性很强（r = 0.78，P < 0.001），而常绿针叶树中则无相关性（r = 0.03，P > 0.25）。与具有相同叶片N（基于质量或面积）的落叶树相比，常绿树的A和SLA较低。对于所有汇总数据，基于质量的叶片N和A均与SLA相关（r = 0.6）；相比之下，基于面积的叶片N与SLA紧密相关（r = 0.81），但基于面积的A则不然（r = 0.06），这是因为常绿针叶树中单位N的A较低。对所有汇总数据进行的多元回归分析表明，基于质量（r = 0.80）和面积（r = 0.55）的N（基于质量或面积）和SLA分别与A显著相关（P < 0.001）。这些结果进一步证明，对于具有不同叶片特征组合的生态上不同的物种组，A - N关系存在根本差异：叶片寿命长且SLA低的物种，无论是阔叶还是针叶，每单位叶片N的A往往较低，A - N关系的斜率较低且截距较高，而叶片寿命较短且SLA较高的物种则相反。一个单一的全球A - N方程分别高估和低估了温带树木在其叶片N范围上限和下限的A。在对不同生态系统的光合作用进行建模时使用A - N关系的用户应了解基于不同物种分组的回归方程的优点和局限性。
